The present invention relates to a plasma reactor for performing a gas treatment for air purification and the like by generating low temperature plasma through streamer discharge and purification equipment using the plasma reactor, and more particularly, it relates to a technique to generate low temperature plasma in a wide region through discharge.
A plasma reactor utilizing low temperature plasma has been conventionally used in air purification equipment or gas treatment equipment that decomposes a toxic component or an odor component included in, for example, air or exhaust gas by using the function of active species generated by plasma so as to make such a component innocent or odorless. For example, Japanese Laid-Open Patent Publication No. 8-155249 or 9-869 discloses an apparatus in which a plurality of needle-shaped electrodes working as discharge electrodes are disposed substantially perpendicular to a plate-shaped electrode working as a counter electrode and plasma is generated by causing streamer discharge between the discharge electrodes and the counter electrode, so as to perform a gas treatment with a target gas introduced into the discharge field.
When the streamer discharge is caused in the aforementioned manner, a narrow column-shaped space between each discharge electrode and the counter electrode corresponds to the discharge field. The discharge field is formed with respect to each of the discharge electrodes, and each discharge field has a comparatively small region. Therefore, in the apparatus disclosed in each of the aforementioned publications, the discharge electrodes are densely arranged in one or more lines, so as to increase a plasma generation region by suppressing gaps made between the plural discharge fields formed between the respective discharge electrodes and the counter electrode.
The aforementioned architecture, however, is complicated because a large number of discharge electrodes should be densely arranged.
Accordingly, if the discharge field corresponding to each discharge electrode can be increased, the plasma generation region can be increased even when the number of discharge electrodes is reduced. For example, when a steep pulse high voltage having a pulse rise time as short as approximately 100 ns or less and a pulse width of approximately 1 μs or less is applied between a discharge electrode and a counter electrode, plasma can be generated in a comparatively wide region.
This is for the following reasons: 1) Since the application time of the voltage is short, a high voltage that may cause a spark in general discharge can be instantaneously applied; 2) discharge can be easily caused all over the place when the application voltage is high; 3) the voltage rise is so steep that the discharge is less suppressed by the space charge effect; and 4) the rise time is so short that homogenous discharge can be easily caused.
When a pulse power source for supplying such a steep pulse high voltage with a small pulse width is used, however, the scale of the whole equipment is large and hence the cost is high. Furthermore, the discharge can be caused merely during a short time corresponding to a very small pulse width, and therefore, the time for generating the plasma is also short, resulting in lowering the efficiency of the gas treatment.
The present invention was devised in consideration of these disadvantages, and an object is increasing a plasma generation region formed through streamer discharge without making the architecture of a plasma reactor complicated and without increasing the cost.